Purification of crude anthracene



% Anthrocene in Product Anthrocene in Product K. R. NICKOLLS ET AL 2,783,287

PURIFICATION OF CRUDE ANTHRACENE Filed Sept. 29, 1952 Q Anthrocene in Product El Recovery of Anthrocene 0 2 4 6 8 I0 l2 l4 l6 I8 20 22 Water in Solvent (Acetone) Anthrucene in Product El Recovery of Anthrocene O 2 4 6 8 IO I2 l4 I6 I8 20 22 Water in Solvent (Methyl Ethyl Ketone) BDY ATTORNEYS Fig. 2.

United States a PURIFIcATIoN OF CRUDE ANTHRAtIENE Application September 29, 1952, Serial No. 311,978

6 Claims. (Cl. 260-675) The present invention relates to anthracene and particularly to an improved process of recovering anthracene to the trade as"anthra'cene salts. I ,"The presence of impurities in crude anthracene having characteristics similar to those of anthracene has rendered the production of reasonably pure anthracene expensive and difficult. The coal tar crudes, i. e., anthracene salts, from which anthracene is recovered is of variable composition and ranges from -45% anthracen'e; '6-20% carbazole, and the balance phenanthrene, with some fiuorene, acridine, hydroacridine, acenaphthene, diphenyl methyl anthracene, pyrene, chrysene, retene, fluoranthene, ch'rysogen, high boiling parafiins, such as eicosane, docosane, and the like. Other impurities are sometimes also present in small amounts. The relative proportions of the different impurities vary somewhat with the nature of the'coal from which the crude anthracene is produced.

Crude anthracene presscake, which may contain from less than 20 to 60% of anthracene, is usually purified by of substantially high purity from coal tar crudes known I various methods of fractional solubility, or by causing some of the major impurities to react with chemicals which transform them into insoluble or non-volatile products which can then be easily separated. The processes at present in use for the most part use solvents, such as pyridine, tetrahydrofurfuryl alcohol, o-dichlorobenzene, 4-hydroxy-4-methyl-Z-pentan-one, carbon tetrachloride, solvent naphtha, creosote oil, petroleum hydrocarbons and the like, and by these methods the crude anthracene may be purified, leaving mainly carbazole and phenanthrene as impurities. The processes are very costly, and troublesome, and in the case of pyridine the odor is extremely unpleasant.

One method which has been used consists of grinding crude anthracene in a ball or pebble mill with a snfii-cient quantity of solvent, such as benzol, crude coal tar solvent, carbontetrachloride 'and the like to dissolve high boiling paraflins and phenanthrene but which do not appreciably dissolve the anthracene, and carbazole. The grinding is continued for a period of time until the crude anthracene has become very finely pulverized or sub-divided. In order to dissolve substantially all of the high boiling paratfins, it is essential that two or more grinding treatments with solvent be employed. This operation alone is time consuming and requires a minimum of 4 to 6 hours. At the conclusion of the grinding operations and solvent action, the contents of the mill. are discharged and filtered.

The remaining residue is washed several times with the same solvent or solvents and dried. The removal of carbazole from the ground and partly refined anthracene is accomplished by solvent extraction with either acetone or pyridine. The best possible yield of anthracene obtainable according to this procedure is about 72% of Another method consistsv of extracting the crude anthrace'ne by the action of sulfur dioxide, aqueous ammonia containing at least ammonia in solution, methyl and ethyl ethers, acetone and the like. Regardless of the extracting medium employed, the extraction must be repeated for at least 13 to 36 times at specified volumes of solvent until the anthracene is purified to the desired extent. After the anthracene ha been treated with the solvent to remove the desired amount of impurities, the solvent remaining in contact with the anthracene must be removed by either heating the anthracene to a sufiicient temperature to evaporate the solvent, or by treatment with steam which is blown through or over the anthracene to expel the solvent. .When steam is employed, the mixture of steam and solvent, for example, acetone, must be cooled to condense the water-acetone mixture.

The recovery of anhydrou acetone for recycling into the extraction system poses a serious problem. It is well known that the production of relatively anhydrous acetone is a difficult process to achieve economically because a pinch occurs in the acetone rich portion of vapor-liquid equilibrium phase diagram of the acetone: water system. Large amounts otheat are required to remove the water and the relatively high reflux ratios re-, quired to produce a recovered solvent containing low water concentrations result in the use of large sized distillation columns, excessive amounts of cooling water, etc.

All of the foregoing, processes are expensive, slow, inetlicient, and require a great deal of time, labor and equipment. Accordingly, it is an object of the present invention to overcome these shortcomings and to provide a less expensive and more efiicient method of recovering high purity anthracene from coal tar crudes involving solvent leaching followed by distillation.

In accordance with the present invention, the improved method involves two purification steps. The first is leaching of the solid anthracene salts with a solvent at a temperature ranging from 15 to 30 0., preferably at or near room temperature, to remove substantially all phenanthrene, fiuorene, and carb-azole. The solid product, after adhering solvent has been removed by heating at a temperature ranging from 55 to 295 G, contains -90% anthracene. The second step is a fractional distillation of the leached crude in a conventional manner which produces a product having a purity of -98% anthracene or better and which is suitable for production of high purity anthraquinone by oxidation of the anthracene in the conventional manner.

The solvent employed is one which has high solubility for the impurities, i. e., phenanthrene, fiuorene, c-arbazole, etc, and low solubility for anthracene. As examples of such solvents, the following may be mentioned:

Alcohols methanol l-pentanol ethanol Z-pentanol propanol l-hexanol isopropanol ethanol chlorhydrin n-butanol furfuryl alcohol sec.-butanol I isobutanol Amides formamide dimethyl formamide Amines aniline monoethanolamine Miscellaneous nitrogen compounds acetonitrile nitromethane Acids acetic lactic diethylene glycol triethylene glycol trimethylene glycol Phenanthrene and fluorene are considerably more soluble in these solvents than are carbazolc and anthracene. However, all of the foregoing solvents and mixtures thereof show a high ratio for the solubility of carbazole relative to anthraccne. The foregoing solvents are readily recovered from the solid product and from the spent leaching solvent for reuse. They are thermally stable and have a boiling point below 250 C. Moreover, they are all liquids at room temperature. Of all the foregoing solvents, we prefer to employ acetone and methylethyl ketone because of their availability, cheapness, and ability to produce a leached solid having high anthracene content and because of their low boiling points which facilitate their recovery by distillation processes. In addition, the latter solvents can be used efiectively in the presence of 520% of water for the recovery of anthracene from the crude anthracene salts. This is extremely important because it results in significant economies in the recovery of these two solvents.

Another advantage of using water in the solvent, not only in-acetone or methylethyl ketone, but in all the others listed above, is the increase of the recovery of the anthracene. The increase in recovery rises as the percent of Water in the solvent increases with a maximum re covery at 20% water content in the solvent. The actual recovery is 90% of 80-90% purity or 72% yield of anthracene. product to distillation yields anthracene of 95-98% purity. The anthracene is of such high purity that upon oxidation, it yields anthraquinone of 99% purity in a yield of 92% of theory. he anthraquinone is used success'fully to prepare l-amino-anthraquinone of acceptable quality. This indicates that the anthracene is of such quality that it may be used in manufacture of anthraquinone-type dyestutfs.

In practicing the present invention, one part by weight of any crude anthracene salts containing from 24 to 45% anthracene is agitated in a vessel at a temperature of 20 to 35 C. with 1.5, 2.0, 3.0, or 4.0 parts by weight, preferably 2.5 parts by weight, of any one of the foregoing solvents of technical grade or mixtures thereof for a period of time ranging from l to3 hours. The slurry is filtered and the solid product dried by any conventional means.

The leached erudeproduct is a light green to light greenbrown color and has a bright green fluorescence when viewed under ultraviolet light. During the leaching operation essentially all of the compounds which have lower boiling points than anthracene, along with most of the carbazole which has a higher boiling point than the anthracene, are removed. The leached product which is then stripped of the major components, i. e., phenanthrene, carbazole and a number of lower boiling components, is readily susceptible to fractional distillation during which most of the compounds having boiling points higher than that of anthracene, including substantially all of the carbazole and naphthacene, are completely re- H moved. In general, however, to achieve purities of 98% subjecting the leached or solvent extracted L of anthracene or better, the minimum number of theoretical plates required will be 10 to 50 and the minimum reflux ratio of 2 to 3. In order to achieve the production of at least 95-98% of pure anthracene, we prefer to employ a distillation column having approximately 50 theoretical plates at a pressure in the range of 100 to 600 mm. of mercury absolute and a pot temperature in the range of 265 to 360 C. and a head temperature of 250 to 330 C. Any conventional distillation column having the required number of plates may be employed. The distillation step removes all traces of the green fluorescence which is attributable to the presence of naphthacene. The resulting distilled product is white to light yellow in color and fluoresces to blue when viewed under ultraviolet light.

The leaching or solvent extraction may be carried out as a single stage process, a multi-stage process, or continuously. The multi-stage or continuous process may be cocurrent with regard to the relative direction of flow of solid and solvent. The multi-stage operation may be carried out in a single unit or in multiple units, all modifications being based chiefly on the economics of the overall process. A higher purity product and improved recovery of anthracene is obtained by the use of countercurrent multi-stage type of equipment. Equipment of this type is illustrated by G. G. Brown in his text Unit Operations published by John Wiley & Sons, 1950, and the schematic flow diagrams together with a description illustrated by Perry on pages 1216-1220 in his Chemical Engineers Handbook, second edition.

The foregoing two-step process is much more effective than a two-step process involving solvent extraction and sublimation as the second step. In the latter process, all the impurities in the leached crude, particularly carbazole, tend to sublime/along with the anthracene to a degree sufficient to seriously impair the purity of the final product.

The two-step process in accordance with the present invention is very critical as established by the following facts:

(1) Solvent extraction without distillation of crude anthracene does not lead to a higher purity product and improved recovery.

2) Distillation alone of crude anthracene does not lead to purified anthracene of suitable purity for dyestui'f manufacture.

To obtain a product of high purity and improved recovery it is essential that our two steps be carried out in the order prescribed. If the process is carried out in the reverse manner, i. e., distillation followed by solvent extraction, sufficiently pure anthracene is not obtained for the manufacture of dyestuffs.

The two graphs constituting the accompanying drawing illustrate the relationship of the purity of anthracenc to the percent of water in the extracting solvents. Fig ures l and 2 show this relationship with acetone and methylcthyl. ltetone, respectively.

By reference to Figure I, it will be obsewed that while anhydrous acetone may at first appear to be desirable. a water content of 4.5% in the acetone can be readily tolerated without appreciably lowering the purity of the anthraccne product while at the same time the anthracene recovery is improved. In addition, as pointed out above.

' this is highly desirable since in the recovery of acetone and inethylcthyl kctone, it is difiicult to remove the last traces of water during distillation.

Figure 2 shows that as much as 10% of water in methylethyl lzetone can be tolerated without appreciably lowering the purity of the anthracene product, while at the same time, the anthracene recovery is improved.

From the foregoing description, it becomes manifest that depending upon the solvent, i. e., anhydrous or containing water, it is possible to obtain about recovery of anthracene withabout purity or 72% yield of anthraeene as well as about 90% recovery with 80% purity or 72% yield of anthracene. By subjecting the leached product to the distillation step, the two-step process produces a final product :of 95-98% purity.

The following examples describe in detail the methods for accomplishing the above objects, but it is to be understood that they are inserted merely for the purpose of illustration and are not to be construed as limiting the scope of the invention.

EXAMPLE I 5,000 grams of crude anthracene salts containing 42% anthracene were agitated at 30 C. with 12,500 grams of technical grade acetone for 2 hours. The slurry was filtered and the solid product dried. The solid product weighed 2,021 grams and was found to contain 85% anthracene as analyzed by the maleic anhydride adduct method.

1,650 grams of the above leached crude were distilled at 200 mm. pressure of mercury absolute in a distillation column having approximately 50 theoretical plates with a pot temperature of 280 C. and a head temperature of 270 C. The distillate included 1,234 grams of a material having a White color and containing 95.4% anthracene.

EXAMPLE II Example I was repeated with the exception that 12,500 grams of technical grade acetone were replaced by an equivalent amount of technical grade of methylethyl ketone containing 10% of water. After distillation, the distillate included 1,259 grams of a material having a white color and containing 97% anthracene.

EXAMPLE III Example I was again repeated with the exception that 12,500 grams of technical grade acetone were replaced by an equivalent amount of technical grade acetone containing 4 to 5% of water. After distillation, 1,286 grams of a material having a white color and containing 98% of anthracene was obtained.

We claim:

1. The process of purifying crude anthracene salts containing 24 to anthracene which consists of extracting the impurities therefrom with a solvent selected from the group consisting of liquid alkanols, liquid ketones, and liquid glycols having 1 to 4, 3 to 7, and 2 to 6 carbon atoms, respectively, the said solvent containing from about 5 to about 10% water, at a temperature ranging from 20 to 35 C., filtering and drying the extracted crude, and then subjecting it to a fractional distillation in a multiplate column at a selected pressure of to 600 mm. of mercury at a selected pot temperature of 265 to 360 C. and a selected head temperature of 250 to 330 C., which selected temperatures are above the boiling point of the anthracene at the selected pressure.

2. The process according to claim 1, wherein the solvent is acetone.

3. The process according to claim 1, wherein the solvent is acetone containing about 5% of water.

4. The process according to claim 1, wherein the solvent is methylethyl ketone.

5. The process according to claim 1, wherein the solvent is methylethyl ketone containing about 10% of water.

6. The process according to claim 1, wherein the solvent is diethylene glycol.

References Cited in the file of this patent UNITED STATES PATENTS 1,879,686 Jaeger et a1 Sept. 27, 1932 1,905,903 Jaeger et al. Apr. 25, 1933 2,137,499 Moravec Nov. 22, 1938 2,213,755 Yule Sept. 3, 1940 FOREIGN PATENTS 499,940 Belgium June 9, 1951 OTHER REFERENCES Clark, Ind. & Eng. Chem., vol. 11 (1919), pages 204- 209.

Khadzhinov et al.: Org. Chem. Ind. U. S. S. R., vol. 4 (1937), pages 34553. Abstracted in Chem. Abs., vol. 32, pages 4976 (1938).

Davis et al.: Jour. Am. Chem. Soc., vol. 64, pages 108-10 (1942). 

1. THE PROCESS OF PURIFYING CRUDE ANTHRACENE SALTS CONTAINING 24 TO 45% ANTHRACENE WHICH CONSISTS OF EXTRACTING THE IMPURITIES THEREFROM WITH A SOLVENT SELECTED FROM THE GROUP CONSISTING OF LIQUID ALKANOLS, LIQUID KETONES, AND LIQUID GLYCOLS HAVING 1 TO 4, 3 TO 7, AND 2 TO 6 CARBON ATOMS, RESPECTIVELY, THE SAID SOLVENT CONTAINING FROM ABOUT 5 TO ABOUT 10% WATER, AT A TEMPERATURE RANG- 